As the inner liner layer of a pneumatic tire, a rubber layer containing a butyl rubber as the main component is generally used. In response to the recent requirement for saving the weight of a tire, the use of a thin resin film having low-gas permeability is proposed.
Conventionally, a method of producing a pneumatic tire formed by using this resin film as an inner liner includes sequentially wrapping and overlaying a resin film around a tire molding drum and then a member such as a carcass and a tread formed of an unvulcanized rubber around the resin film, removing the drum to obtain a green tire, and vulcanizing this green tire by heating to obtain a pneumatic tire (for example, Paragraph 0042 of Patent Document 1).
However, since there is no adhesion caused by covulcanization between the carcass formed of an unvulcanized rubber and the resin film, a problem arises in that the carcass and the resin film may be separated. A laminate formed by lining a resin film with a rubber layer may be previously prepared. However, when this laminate is wrapped around a tire molding drum, the resin film on the one side and the rubber layer on the other side are overlapped at the both ends of this laminate but may be separated.
To solve the problem of the separation of the resin film and the carcass, various technologies are proposed.
For example, Patent Document 2 proposes a technology using a resin film formed in a cylindrical shape without an adhesion part to form an inner liner layer.
Patent document 3 proposes a technology wrapping a laminate formed by lining the surface of a resin film with a rubber layer around a tire molding drum and overlapping and bonding the both ends of this laminate to an adhesive layer used for ends.
Patent document 4 proposes a laminate formed of a thermoplastic resin film, an adhesive layer on the surface of the thermoplastic resin film, and a rubber sheet displaced in the length direction against applied to this adhesive layer. The surface of the adhesive layer and the back surface of the rubber sheet are exposed at one end and the other end of this laminate, respectively. When this laminate is wrapped around a tire molding drum, the adhesive layer at one end of this laminate is bonded to the rubber sheet at the other end to prevent the overlapping part of the laminate from being separated.
The technologies of Patent Documents 1 to 4 have problems of the separation of the overlapping part of a laminate, the increase in stock management cost, the decrease in production efficiency, the increase in the number of components, the deterioration of wrapping workability around a molding drum, and the like.
Specifically, according to Patent Document 1, as stated, the overlapping part may be separated when a laminate is wrapped around a tire molding drum.
According to Patent Document 2, cylindrical thermoplastic resin films with various sizes depending on the sizes of tires are required to be prepared, arising problems of the increase in stock management cost, the decrease in production efficiency, and the like.
According to Patent Document 3, the number of components increases for the adhesive layer used for ends. Moreover, it needs additional work to transfer and laminate this adhesive layer used for ends.
According to Patent Document 4, since the layers of the laminate are displaced and laminated, the lamination requires additional work. Moreover, since the adhesive layer is exposed at one end in the length direction, the wrapping workability around a molding drum is poor.
The inner surface of the tire in which gas is to be filled has an inner liner disposed as a gas barrier layer blocking off gas. In recent years, a technology using a thermoplastic resin film with a small amount of oxygen permeation, i.e., a high gas barrier property, and a weight lighter than conventional butyl rubbers as an inner liner is proposed (for example, see Patent Document 5).
In Patent Document 5, setting the storage modulus of the layer of a diene rubber composition (carcass) smaller than that of the layer of a thermoplastic resin elastomer composition (thermoplastic resin film) in combination with setting the storage modulus of an adhesive bonding these layers to a value intermediate between those of the layers prevents the stress concentration caused by the deformation of a tire from occurring to the thermoplastic resin film and improves the low temperature durability of the thermoplastic resin film.
However, there is still a room for improvement in the tire disclosed in Patent Document 5. In a tire formed by using a thermoplastic resin film as an inner liner, the following property of the inner liner to the deformation of the tire decreases, for example, in a low-temperature environment of −20° C. or less compared with about 0° C. Therefore, in the adhesive interface between the inner liner and the carcass, the stress on the inner liner may further severely increase to cause the higher probability of fractures and cracks of the inner liner.
Accordingly, for example, in a low-temperature environment of −20° C. or less, the inner liner and the carcass are required to be further softened. However, too much softened carcass has a problem of the decreased durability of the entire tire. A tire capable of delivering sufficient performance can be provided if the probability of fractures and cracks of the inner liner can be maintained low without the durability of a tire being sacrificed even in the above-mentioned low-temperature environment.